This invention relates generally to color television cameras, and more particularly to the automatic correction of registration errors.
Color television cameras generally comprise multiple image pick-up devices, e.g., tubes, that generate separate video signals representative of component colors of a scene being viewed by the camera. The necessity for accurate registration, i.e., synchronization, of the video signals produced by a color television camera so that the signals simultaneously convey information related to the same portion of an image is well known, and the prior art is replete with various automatic registration systems for this purpose.
Many known automatic registration systems require the use of a special registration set-up chart (or a diascope inside of the camera lens) to enable a predeterMined pattern of figures to be imaged onto the pick-up devices of the camera, and registration is performed as part of the normal camera set-up procedure prior to going "on-air". As the pattern is scanned, transitions in the video signals associated with the edges of the figures are compared, and correction signals are applied to the scan circuits of the camera so that corresponding transitions in the different video signals occur simultaneously. The correct operation of many such systems is dependent upon the existence of video signal transitions in predetermined regions of the raster and, in some cases, upon transitions between full black and full white levels. Over a period of time, however, registration can change, because of temperature or voltage changes, or because of drift in electrical circuits, and the camera must be taken "off-air" to readjust the registration.
Although there are automatic registration systems that operate on-air to correct registration errors, those systems have limited capability or have other disadvantages which have limited their usefulness. It is desirable to provide improved systems and methods that are capable of operating on-air with live or actual scenes to automatically detect and correct registration errors in color television cameras, and it is to this end that the present invention is directed.